1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and mote particularly, to a liquid crystal panel having a dual column spacer structure and a manufacturing method thereof.
2. Discussion of Related Art
A liquid crystal display device displays images by employing the optical anisotropy and birefringence properties of liquid crystal molecules. A typical liquid crystal display device includes two opposing substrates each having electric field generating electrodes disposed on a surface facing the other substrate. A liquid crystal layer is formed between the two substrates. The orientation of liquid crystal molecules of the liquid crystal is then changed by means of an electric field generated by applying a voltage to the two electrodes. When the orientation of the liquid crystal molecules is changed by the electric field the transmission of light through the liquid crystal layer changes due to the optical anisotropy and birefringence properties of the liquid crystal. Accordingly, the amount of light that transmitted through the liquid crystal display device can be controlled to display a desired image. A liquid crystal display device typically includes a Thin Film Transistor (TFT) as a switching element of the liquid crystal display (LCD).
FIG. 1 is a perspective view schematically showing the construction of a liquid crystal display device of the related art. Referring to FIG. 1, the liquid crystal panel provided within the liquid crystal display device has a first substrate 10 and a second substrate 20, which are bonded together with a predetermined distance or gap therebetween, and a liquid crystal layer 30 formed between the first substrate 10 and the second substrate 20.
The first substrate 10 includes a plurality of gate lines 13 and a plurality of data lines 12 are arranged on a transparent glass substrate 11. The plurality of gate lines 13 are arranged to be substantially parallel to each other and separated by a predetermined distance. The plurality of data lines 12 are arranged substantially perpendicular to the gate lines 13. Pixel regions (Pixel) are defined by the crossings of the data lines 12 and gate lines 13.
Furthermore, a pixel electrode 14 is formed in each pixel region (Pixel). A TFT is formed at each crossing of a gate line 13 and a data line 12. The TFT applies a data signal of the data line 12 to each pixel electrode 14 according to a scan signal applied through the gate line 13.
The second substrate 20 includes black matrix layers 22 for shielding light from portions of the substrates other than the pixel regions (Pixel) formed on a second transparent glass substrate 21. R, G, and B color filter layers 23 for displaying colors are formed at portions corresponding to the pixel regions. A common electrode 24 for generating electric fields with the pixel electrode is formed on the color filter layers 23.
Charge capacitors CST connected in parallel with each pixel electrode 14 are formed on gate lines 13. A portion of a gate line 13 is used the first electrode of a charge capacitor CST. Metal patterns of an island shape, which are formed using the same material as that of source and drain electrode, are used as second electrodes of the charge capacitors CST. A passivation layer may be formed over components on the first substrate including the TFT and the charge capacitors CST.
In the related art liquid crystal display device described above, molecules of the liquid crystal layer 30 disposed between the first substrate 10 and the second substrate 20 are oriented by means of an electric field between the pixel electrodes 14 and the common electrode 24. The amount of light that transmitted through the liquid crystal layers 30 changes with the orientation of the liquid crystal layer 30 to display a desired image.
A liquid crystal display device constructed as described above is called a Twisted Nematic (TN) mode LCD. The TN mode LCD is disadvantageous in that it has a narrow viewing angle. An In-Plane Switching (IPS) mode LCD has been developed to overcome the narrow viewing angle disadvantage of the TN mode.
In the IPS mode LCD, the pixel electrodes and the common electrode are formed in the pixel regions on the first substrate. The pixel electrodes are arranged parallel to the common electrode with a predetermined distance therebetween so that a horizontal electric field is generated between the pixel electrodes and the common electrode. The liquid crystal layer is oriented by the longitudinal electric field.
In the liquid crystal display devices described above, spacers (not shown in the drawings) for maintaining the gap between the two substrates are formed between the first substrate 10 (for example, an array substrate) and the second substrate 20 (for example, a color filter substrate). The spacers are classified into spacers of a spherical shape, which are disposed on a substrate using a dispersing method, and spacers of a column shape (column spacer), which are directly formed on the color filter substrate 10 and the array substrate 20.
A column spacer construction having a dual structure, referred to as a dual column spacer has been proposed. The dual column spacer includes a first column spacer and a second column spacer. The first column spacer serves to maintain the gap through contact with both the first substrate 10 and the second substrate 20. The second column spacer is separated from one of the first or second substrate 10 or 20 by a predetermined distance, and serves as a pressing spacer to preserve a marginal gap between the substrates when a surface of the liquid crystal device is moved by the spaced distance.
FIG. 2A is a cross-sectional view of the liquid crystal panel to which the dual column spacer structure of the related art is applied and FIG. 2B is a cross-sectional view of the liquid crystal panel having the thick organic insulation film.
Referring to FIGS. 1 and 2A, on the first substrate 10 are defined the TFT region (i.e., the switching region), the pixel region (Pixel), and the storage region CST.
A TFT having a gate electrode 41, an active layer 13a, a source electrode 12a, and a drain electrode 12b is formed in the TFT region. A transparent pixel electrode 14 is formed in the pixel region (Pixel).
The charge capacitor CST is formed in the TFT region. The charge capacitor CST uses the gate line 13b as the first electrode and is formed over the gate line 13b in an island shape. Furthermore, the charge capacitor CST uses a metal pattern 12c contacting the pixel electrode 14 as the second electrode. The charge capacitor CST may have a variety of structures and shapes. An insulating layer 42 is formed between the first and second electrodes of the charge capacitor CST.
The black matrix layers 22 are formed on one surface of the second substrate 20 in an area corresponding to the TFTs, and the gate lines 13 and the data lines 12 of the first substrate. The second substrate 20 is spaced apart from the first substrate 10 and a liquid crystal layer 30 is formed therebetween. The color filter layers 23 are formed on a portion of the surface of the second substrate 20 corresponding to the pixel regions (Pixel). A transparent common electrode 24 is formed on the entire surface of the second substrate 20 on which the color filter layers 23 and the black matrix layers 22 are formed. Orientation films (not shown) may be formed on the pixel electrodes 14 and the common electrode 24, respectively. A detailed description of the orientation films will be omitted.
First and second column spacers 50a and 50b are formed below the common. electrode 24 corresponding to the TFT and a portion of the pixel region (Pixel). The spacers may have a ball or column shape. FIG. 2A shows spacers 50a and 50b of a column shape. Column-shaped spacers have the advantage of having a relatively small adverse effect on the aperture ratio when compared with ball-shaped spacers.
The first and second column spacers 50a and 50b are uniformly distributed over the entire surface of the second substrate 20. The first column spacer 50a and the second column spacer 50b have the same length since first column spacer 50a and the second column spacer 50b are each fabricated using the same process. The first column spacer 50a serves as a gap spacer that maintains the gap between the two substrates 10 and 20. The second column spacer 50b is spaced apart from the first substrate 10 by a predetermined distance. The first column spacer 50a is positioned to contact a feature on the first substrate 10 having a step height above the first substrate 10.
Accordingly, the first column spacer 50a may be formed in an area corresponding to the TFT (i.e., an elevated portion) and accordingly directly serves to maintain the gap between the first substrate 10 and the second substrate 20. However, the second column spacer 50b is not formed in an area corresponding to an elevated portion such as the TFT, and may accordingly be separated from the first substrate 10 by a predetermined distance.
The second column spacer 50b is separated from one of the first substrate 10 and the second substrate 20 by a predetermined distance. Therefore, if the liquid crystal is excessively filled between the substrates, the liquid crystal may flow into the space between the second column spacer 50b and the first substrate 10. Accordingly, the second column spacer 50b can minimize the occurrence a gravity induced failure in which the liquid crystal flows downwardly out of the panel. The second column spacer 50b can also prevent pressing spots of the liquid crystal panel by serving as a force resistance component when pressure is applied to the liquid crystal panel. Furthermore, the second column spacer 50b functions to preserve or increase a minimum spacing between the first and second substrates 10 and 20 when forming the liquid crystal layer by injecting liquid crystal therebetween the first and second substrates 10 and 20.
The first and second substrates 10 and 20 are fabricated separately. After the first and second substrates 10 and 20 are fabricated separately, the substrates are bonded together to complete the liquid crystal panel.
A photo acryl pixel structure has recently been widely used to improve the aperture ratio of the liquid crystal panel. The photo acryl is employed in the form of a thick organic insulation layer.
Referring to FIG. 2B, a photo acryl layer 44′ is formed as a relatively thick organic insulation layer on the completed lower substrate 10 and is then polished. However, it is difficult to use the photo acryl layer 44′ with the dual column space structure of the related art. When the photo acryl layer 44′ is formed on the first substrate 10, the second substrate 20 and the first substrate 10 having the first column spacer 50a and the second column spacer 50b; with the same height as described above cannot be bonded together because no elevated step height feature is formed on the first substrate 10. The first column spacer 50a indicated by reference numeral “A” can serve as the gap spacer without change even when the photo acryl layer 44′ is formed, but the second column spacer 50b indicated by reference numeral “B” and having the same height as that of the first column spacer 50a cannot be separated from the first substrate 10 by a predetermined distance. Accordingly, the second column spacer 50b cannot serve as the pressing spacer.